The present invention relates to radiation delivery catheters for percutaneous transluminal use. More particularly, the present invention relates to low profile catheter shaft designs for facilitating placement and centering of a radiation delivery wire within a body lumen.
A wide variety of interventional procedures have been developed which require access to remote parts of the vascular system. One increasingly utilized coronary revascularization procedure, for example, is percutaneous transluminal coronary angioplasty (PTCA). In a typical PTCA procedure, a guiding catheter having a prebent distal tip is percutaneously introduced at a remote location such as the femoral artery using a conventional Seldinger technique. The guide catheter is advanced retrograde until it reaches the ascending aorta with the distal tip seated in the ostium of a desired coronary artery. Steering is accomplished during transluminal advancement by torquing the proximal end of the guide catheter as needed until the distal tip is positioned in the ostium.
An elongate, flexible guidewire is then advanced through and out the distal end of the guide catheter, and negotiated through the tortuous vasculature of the coronary arteries until it crosses a lesion to be dilated. A dilatation catheter is thereafter advanced along the guidewire until the dilatation balloon is positioned within the lesion.
Once properly positioned, the balloon is inflated one or more times to an inflation pressure on the order of six to twelve atmospheres or higher to dilate the lesion. Balloon catheters sized for the coronary arteries may inflate to a diameter in the range of from about 2 mm to about 4 mm. Following dilatation, the balloon is deflated and the catheter is proximally withdrawn from the patient.
Approximately 300,000 PTCA procedures were performed in the United States in 1990 and nearly one million procedures worldwide in 1997. The increasing popularity of the PTCA procedure is attributable to its relatively high success rate, and its minimal invasiveness compared with coronary by-pass surgery. Patients treated by PTCA, however, suffer from a high incidence of restenosis, with about 35% or more of all patients requiring repeat PTCA procedures or by-pass surgery, with attendant high cost and added patient risk. Other revascularization procedures such as laser angioplasty and rotational atherectomy appear to also trigger a restenosis initiating response.
Recent attempts to prevent restenosis by use of drugs, mechanical devices, and other experinental procedures have had limited long term success. Stents, for example, dramatically reduce acute reclosure, and slow the clinical effects of smooth muscle cell proliferation by enlarging the minimum luminal diameter, but otherwise do nothing to slow the proliferative response to the angioplasty induced injury.
Restenosis is now believed to occur at least in part as a result of injury to the artenal wall during the lumen opening angioplasty procedure. In some patients, the injury initiates a repair response that is characterized by hyperplastic growth of the vascular smooth muscle cells in the region traumatized by the angioplasty. Intimal hyperplasia or smooth muscle cell proliferation narrows the lumen that was opened by the angioplasty, regardless of the presence of a stent, thereby necessitating a repeat PTCA or other procedure to alleviate the restenosis.
Preliminary studies indicate that intravascular radiotherapy (IRT) has promise in the treatment or long-term control of restenosis following angioplasty. IRT may also be used to prevent or delay stenosis following cardiovascular graft procedures or other trauma to the vessel wall. Proper control of the radiation dosage, however, appears to be important to inhibit or arrest hyperplasia without causing excessive damage to healthy tissue. Overdosing of a section of blood vessel can cause arterial necrosis, inflammation and hemorrhaging. Underdosing will result in inadequate inhibition of smooth muscle cell hyperplasia, or even exacerbation of hyperplasia and resulting restenosis. Thus, a variety of radiation delivery devices have been devised.
U.S. Pat. No. 5,059,166 to Fischell discloses a radioactive stent that is permanently implanted in the blood vessel after completion of the lumen opening procedure. Close control of the radiation dose delivered to the patient by means of a permanently implanted stent is difficult to maintain because the dose is entirely determined by the activity of the stent at the particular time it is implanted. In addition, current stents are generally not removable without invasive procedures. The dose delivered to the blood vessel is also non-uniform because the tissue that is in contact with the individual strands of the stent receive a higher dosage than the tissue between the individual strands. This non-uniform dose distribution may be especially disadvantageous if the stent incorporates a low penetration source such as a beta emitter.
Another approach which is both removable and self centering is the radiation delivery balloon. See, for example, U.S. Pat. No. 5,782,742 to Crocker et al. and U.S. Pat. No. 5,947,889 to Hehrlein in which the isotope is carried by the balloon. A variation in which the balloon is filled with a radioactive liquid is disclosed in U.S. Pat. No. 5,616,114 to Thornton et al.
A third approach involves the use of wire sources in which the isotope is carried by a flexible wire or wire like structure. Examples include U.S. Pat. No. 5,199,939 to Dake et al. and U.S. Pat. No. 5,833,593, among others, to Liprie. Used alone, the wire type sources tend to lie off axis in the vessel, producing different delivered dose characteristics in the near wall and the far wall due to absorption and penetration issues. Thus, a variety of centering catheters or structures have been devised in an effort to center the source in the lumen. Unfortunately, centering catheters in general add to the crossing profile of the device and possibly also limit its ability to track through small diameter and/ or tortuous vascular pathways.
Thus, notwithstanding the various efforts in the prior art, there remains a need for an access and/or centering catheter for wire and wire type sources which minimizes the catheter crossing profile while permitting rapid placement and centering of a radioactive source wire at the treatment site.